Australia’s Strategic Defence Update 2020 sets Australia’s Defence priorities to our near region, including the South West Pacific and near north. This shift places a new emphasis on Australia’s northern and eastern coast airfields to support civil and military air operations. While strategic geopolitics plays a major part in this policy reset, one of the greatest risks to regional air power comes not from politics, but from climate change.

As noted in the first of this two-part series on airbases, for the foreseeable future, civil and military aviation will require major airfields. These are typically located near major cities which in turn are predominantly located in coastal regions. These airfields have the characteristics of a two and a half to three kilometre runway, and high pavement strength of around 50 to 60 centimetres in depth. These runway characteristics are likely to remain for many decades, even allowing for advances in engine power and aerodynamic design. Legacy aircraft, that is, those in service now, are project to remain in service for decades.

The location of airfields is determined by the demands of logistics, labour and purpose. These characteristics have seen airfields located in and adjacent to cities that were established on or near the coast when shipping was the dominant form of transport. This exposes airfields to the existential threat of sea level rise and extreme weather events due to climate change.

A 2019 report from the EU-funded Copernicus Flood List observed, ‘Most major airports in Australia are located on reclaimed swamps, sitting only a few metres above the present-day sea level.’ The article went on to note that, ‘the US National Oceanic and Atmospheric Administration (NOAA) recommended that a global mean sea level rise of 2.7 metres should be considered in planning for coastal infrastructure.’ These metrics indicate that Australian aviation is at direct risk of flooding from sea-level rises.

The Actuaries Institute, used in determining insurance, reports that for the last five years Australian East Coast temperatures are already averaging more than one degree hotter than their baseline of the 1980-81 values and is likely to exceed the target of 1.5 degrees exacerbating extreme weather.

The majority of Australia’s East Coast airfields are at risk, as are all of the atoll island airfields of the Pacific. Many of the airfields that were the stepping stones of World War Two’s Pacific theatre will no longer exist, thereby limiting expeditionary air power. On the east coast of Australia, the airfields of Cairns, Townsville, Mackay, Brisbane and Gold Coast-Coolangatta are all less than six metres above sea level. Williamtown and Sydney have airfield elevations of nine metres above sea level.

The relationship is not linear. A sea-level rise of 0.5 metres would see the northern end of Sydney’s Kingsford-Smith main north-south runways and northern taxiways inundated with water. But  airfields on higher-ground than this have already experienced floods. Despite Rockhampton’s airfield being at an elevation of 10 metres, flooding of the Fitzroy River in 2011 2013 and 2017 caused it to be closed for weeks at a time. The Queensland Government’s 2016 Lower Fitzroy River Infrastructure Project Climate and Natural Hazards Report forecasts that extreme weather events will continue to increase the risk of flooding events.

There are other risk factors beyond inundation of water that affect the viability of airports and airfields. Airfield pavements of up to 60 centimetres, typically covering more than twenty hectares of concrete and bitumen, effectively ‘float’ on the subgrade below. Changes in the groundwater table and salinity create uneven upward force, which damages the pavement above. Anecdotally, following minor flooding at Townsville, the removal of a service cover resulted in a metre high column of water bursting out of the ground.

Airfields have significant underground services and infrastructure, including drains, water pipes, power cabling, runway and taxiway lighting, communications, and fuel pipes and lines. Elevated water tables and increased groundwater also increase pollution. Older airfields, in particular, have a legacy of substantial pollution due to fuel, oil, fire-fighting and other chemicals that have leached into the subsoil. The environmental study for Brisbane Airport development noted that the placement of additional material on pavement surfaces not only risked subsidence due the additional material weight, but also forcing contaminated groundwater into adjacent waterways.

Airfields are critical to Australia’s air power capability and economic well-being, and many of these are at risk. Airfields have remarkable and rare characteristics, and are not easily replaced. They are multi-million dollar national assets that require long lead times to either repair or construct alternative sites. Multiple individual studies of airport and airfield viability, along with broader climate change research, indicate that most of Australia’s major airfields are at risk of either inundation or significant damage from climate change. We were expecting a pandemic, but ill-prepared when it occurred; it appears that the same may be the case for our airfields.

Addressing this demands a number of tasks. The first would be a risk analysis of all Australian and South West Pacific airfields to ‘all hazards’ climate change threats, including sea level inundation, water table change, flooding and extreme weather events. Based on that understanding, a risk mitigation strategy could be developed. For many current airfields, there is likely no redundancy or repair option, and alternative would need to be explored. Is it time for the return of the seaplane? Or for increased investment in rotary wing or short field platforms? Whatever the solution, the problem must be identified and explored with a degree of urgency.